Zimbabwean President Robert Mugabe and opposition leader Morgan Tsvangirai agreed Monday to start urgent negotiations toward forming a new government, a first but very tentative step toward ending the nation's political stalemate.

The deal signed on national television was vague, leaving aside nearly every key question about Zimbabwe's future after almost a decade of ruinous decline. But it included clear language vowing an end to state-sponsored political violence, and set a deadline requiring that the talks conclude within two weeks.

Talks were expected to begin Tuesday in the South African capital of Pretoria, wire services reported.

Monday's ceremony -- which included a handshake between Mugabe and Tsvangirai, who had not met face-to-face since Tsvangirai founded the opposition Movement for Democratic Change in 1999 -- generated a rare surge of optimism among Zimbabweans. What remains unclear is whether Mugabe and his ruling clique are prepared to negotiate away a significant share of power after 28 years of nearly total control.

Mugabe, looking drained and glum, described the deal as amounting to an agreement to amend Zimbabwe's constitution and some of its laws. "Our constitution as it is should be amended variously and in a number of ways," he said.

The opposition offered a more expansive vision, portraying the agreement as the framework for negotiating a new government that will resolve Zimbabwe's long-standing political and economic problems, including annual inflation rates that have run into the millions of percent.

"If we put our heads together, I'm sure we can find a solution. Not finding a solution is not an option," Tsvangirai said.

The deal came together under heavy pressure from the African Union, the Southern African Development Community and its appointed mediator, South African President Thabo Mbeki, who flew to Harare, the capital of Zimbabwe, for the signing ceremony. Debate in recent days turned on whether the document would make explicit reference to a transitional authority or a government of national unity, according to two opposition officials familiar with the negotiations. The government, isolated and broke, was eager to reestablish its international legitimacy by signing some kind of deal with the opposition but rejected any references to a "transition" away from Mugabe's rule.

The compromise signed Monday avoided the issue, saying only that the two sides agreed "to a dialogue with each other with a view to creating a genuine, viable, permanent and sustainable solution to the Zimbabwean situation."

Negotiations are nothing new to this troubled southern African nation, once one of the continent's most bountiful and prosperous. Months of talks followed the arrest and beating of Tsvangirai in March 2007, and those negotiations reached several important agreements while also bringing the two sides to the verge of implementing a new constitution.

But the March 29 election, in which Tsvangirai beat Mugabe but by a margin that election officials said required a second round of voting, prompted the government to ignore its concessions as it battled to win the runoff. What followed was months of rising repression, in which Mugabe's regime loosed militias led by army officers onto the opposition. More than 120 activists died in the resulting violence. Tsvangirai boycotted the second vote, on June 27, allowing Mugabe to win easily.

For some opposition activists, the pattern appeared to resemble Mugabe's approach to an earlier challenger to power. A party led by nationalist leader Joshua Nkomo was all but destroyed by massacres in its stronghold, the southwestern Matabeleland region, in the mid-1980s, prompting it to merge with the ruling party in a desperate bid for peace in 1987. Nkomo became a vice president, and several of his deputies took positions in the new government, but power remained firmly in the hands of Mugabe and his security officials.

Tsvangirai's party is attempting to avoid the same fate. Opposition officials say privately that they will agree to join the government only if some key levers of power -- rather than just a few cabinet posts -- are transferred to their control.

They also won an important concession in having Mbeki's role diminished. Opposition officials contended that he favored Mugabe. Though Mbeki was highly visible Monday, mediation will now be overseen by a group that includes Jean Ping, a top African Union official, and United Nations envoy Haile Menkerios.

The talks also will include Arthur Mutambara, head of an opposition splinter faction based mainly in the Matabeleland region. Mutambara also signed the agreement on Monday.

"This is the beginning of the end of Mugabe's rule and influence," said Dumisani Muleya, news editor of the Zimbabwe Independent. "The political and economic fundamentals dictate some transfer of the power."

Yet Mugabe, 84, has long demonstrated formidable survival instincts, first in rising to the top of the 1970s guerrilla movement that forced the white-supremacist regime of Rhodesia from power and, more recently, in holding off repeated challenges to his authority -- including from within his own party.

In each phase so far, he has outmaneuvered or simply outlasted rivals. Among the elements encouraging opposition leaders Monday was the two-week timeline for talks.

"There's a real sense of urgency," said opposition lawmaker David Coltart, who is part of the Mutambara faction of the opposition and is not allied with Tsvangirai. "It's good. It's positive, but there's a long way to go."